Update notes for v0.18.40

Hi folks!

This is just a hotfix update. Updates in this build:

• Fixes a crash which could happen if you selected a scenery item on the very same frame as pressing backspace.
  
• Fixes some spurious error messages which sometimes got displayed while placing NPCs.
  
• Fixes a handful of missing triangles on the south face of the 'arid landmark' building.
  

Thanks for reporting those issues, everyone!

-T